114. Whole Genome Sequencing of Babesia microti from Patients Reveals Recent Origin, Extensive Population Structure, and Recent Expansion of Zoonotic Strains
Session: Oral Abstract Session: Global Health
Thursday, October 8, 2015: 11:15 AM
Room: 32--ABC
Background: Human babesiosis due to Babesia microti is an emerging zoonosis in the United States that causes a febrile syndrome similar to malaria. The origin, genetic diversity, and population structure of existing strains are not understood.

Methods: We sequenced the whole genomes of 22 isolates of B. microti from the continental United States and two isolates of B. microti-like parasites from Alaska and Japan. We constructed a genome-wide map of genetic diversity in this parasite. 

Results: The resulting map contains 2362 single nucleotide polymorphisms (SNPs) among B. microti from the continental United States and demonstrates strong population structure, with at least 4 major populations in the United States and at least 3 clades in New England. The allele frequency spectrum shows a predominance of rare alleles at low frequency, consistent with a recent population expansion. Nucleotide diversity among New England isolates (π = 1.2 x 10^-5) was over 10 times lower than between New England and isolates (π = 3.3 x 10^-4). We estimated the median time to most recent common ancestry at 126 years for Connecticut/ Rhode Island strains (95% HPD 41 – 1125 years), 268 years for Nantucket isolates (95% HPD 102 – 2158 years), 2,213 years (95% HPD 658-19,325 years) for isolates from the Northeast and 10,386 years (95% HPD 2,474 – 72,374 years) for isolates from the continental United States. Comparison to B. microti-like isolates from Alaska and Japan revealed substantial genetic distance and multiple structural genomic rearrangements, suggesting an ancient divergence of these parasites from B. microti in the continental United States. 

Conclusion: Despite initial reports of human babesiosis from Nantucket, genetic data suggest that emergence has occurred simulteneuously from several distinct geographic foci. The CT/RI clade has emerged within the last 200 years and appears to have spread rapidly throughout New England. The split between Midwest and Northeast strains occurred approximately 10,000 years ago.

Jacob Lemieux, MD, DPhil1,2, Alice Tran, B.A.3, Lisa Freimark, MS4, Heidi Goethert, Ph.D.5, Sue Bazner, NP6, Graham Mcgrath, BA6, Eric Rosenberg, M.D.6, Sam Telford, DSc7, Jeffrey Bailey, MD, PhD8 and Pardis Sabeti, MD, DPhil9,10, (1)Department of Medicine, Massachusetts General Hospital, Boston, MA, (2)Infectious Disease Initiative, Broad Institute, Cambridge, MA, (3)Division of Transfusion Medicine, University of Massachusetts Worcester, Worcester, MA, (4)The Broad Institute, Cambridge, MA, (5)Infectious Disease and Global Health, Tufts University School of Veterinary Medicine, North Grafton, MA, (6)Division of Infectious Diseases, Massachusetts General Hospital, Boston, MA, (7)Infectious Disease and Global Health, Tufts School of Veterinary Medicine, Grafton, MA, (8)Medicine, University of Massachusetts School of Medicine, Worcester, MA, (9)Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, (10)Infectious Disease Initiative, The Broad Institute, Cambridge, MA

Disclosures:

J. Lemieux, None

A. Tran, None

L. Freimark, None

H. Goethert, None

S. Bazner, None

G. Mcgrath, None

E. Rosenberg, None

S. Telford, None

J. Bailey, None

P. Sabeti, None

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